The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, the military had accumulated a large collection of incompatible computer networks. Computers on these different networks could not communicate with other computers across their network boundaries.
In the 1960s, the Defense Department wanted to develop a communication system that would permit communication between these different computer networks. Recognizing that a single, centralized communication system would be vulnerable to attacks or sabotage, the Defense Department required that the communication system be decentralized with no critical services concentrated in vulnerable failure points. In order to achieve this goal, the Defense Department established a decentralized standard communication protocol for communication between their computer networks.
A few years later, the National Science Foundation (NSF) wanted to facilitate communication between incompatible network computers at various research institutions across the country. The NSF adopted the Defense Department's protocol for communication, and this combination of research computer networks would eventually evolve into the Internet.
Internet Protocols
The Defense Department's communication protocol governing data transmission between different networks was called the Internet Protocol (IP) standard. The IP standard has been widely adopted for the transmission of discrete information packets across network boundaries. In fact, the IP standard is the standard protocol governing communications between computers and networks on the Internet.
The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also specifies the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the system.
A transmission protocol, called the Transmission Control Protocol (TCP), was developed to provide connection-oriented, end-to-end data transmission between packet-switched computer networks. The combination of TCP with IP (TCP/IP) forms a suite of protocols for information packet transmissions between computers on the Internet. The TCP/IP standard has also become a standard protocol for use in all packet switching networks that provide connectivity across network boundaries.
In a typical Internet-based communication scenario, data is transmitted from an originating communication device on a first network across a transmission medium to a destination communication device on a second network. After receipt at the second network, the packet is routed through the network to a destination communication device, and the TCP/IP protocol determines this routing. Because of the standard protocols in Internet communications, the IP protocol on the destination communication device decodes the transmitted information into the original information transmitted by the originating device.
TCP/IP Addressing and Routing
Under the TCP/IP protocols, a computer operating on an IP-based network is assigned a unique physical address called an IP address. The IP address can include: (1) a network ID and number identifying a network, (2) a sub-network ID number identifying a substructure on the network, and (3) a host ID number identifying a particular computer on the sub-network. A header data field in the information packet will include source and destination addresses. The IP addressing scheme imposes a consistent addressing scheme that reflects the internal organization of the network or sub-network.
A router is used to regulate the transmission of information packets into and out of the computer network. Routers interpret the logical address contained in information packet headers and direct the information packets to the intended destination. Information packets addressed between computers on the same network do not pass through a router on the boundary of the network, and as such, these information packets will not clutter the transmission lines outside the network. If data is addressed to a computer outside the network, the router on the network boundary forwards the data onto the greater network.
TCP/IP network protocols define how routers determine the transmission path through a network and across network boundaries. Routing decisions are based upon information in the IP header and corresponding entries in a routing table maintained on the router. A routing table contains the information for a router to determine whether to accept an information packet on behalf of a device or pass the information packet onto another router.
The IP-Based Mobility System
The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of cellular wireless communication systems using mobile communication devices, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols (e.g. a fixed user location) is violated by the mobility of the user.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a mobile node or mobile station. Typically, a mobile station maintains connectivity to its home network while operating on a visited network. The mobile station will always be associated with its home network for IP addressing purposes and will have information routed to it by routers located on the home and visited networks.
When a mobile station is operating on a home or visited network, specialized servers authenticate, authorize, and collect accounting information for services rendered to the mobile station. This authentication, authorization, and accounting activity is called “AAA,” and AAA computer servers on the home and visited network perform the AAA activities.
Authentication is the process of proving one's claimed identity, and security systems on a mobile IP network will often require authentication of the system user's identity before authorizing a requested activity. The AAA server authenticates the identity of an authorized user and authorizes the mobile station's requested activity. Additionally, the AAA server performs the accounting functions by tracking usage on the network.
Communicating information packets to an AAA server according to an AAA protocol accomplishes AAA. One such protocol is DIAMETER. DIAMETER information packets include a routing header for routing over network connections and attribute value pairs (AVPs). The AVP values designate the type of DIAMETER packet and implementing data instructions.
DIAMETER is a peer-to-peer protocol where any node in a communication system utilizing the DIAMETER protocol can initiate a message or request, which can also include server-initiated messages. A DIAMETER client is a device at the edge of the network performing access control, and the DIAMETER client generates DIAMETER messages requesting AAA services for a user. A DIAMETER agent is a node that does not perform AAA locally such as proxies, redirects, and relay agents. A DIAMETER server performs AAA for the user, and a DIAMETER node can act as either a client or an agent for certain requests.
The focus of the DIAMETER protocol is network access and accounting applications supporting mobile IP systems. However, DIAMETER is designed to be adaptable and extensible by defining new AVPs, creating new AVPs, and creating new AAA applications. DIAMETER AVP values carry specific AAA information and can be used to convey other related control and command functions on the communication system. Compared to earlier standards, DIAMETER features simplified client/user management, Network Access Identifier (NAI) based user authentication, dynamic IP address allocations for mobile stations, dynamic Home Agent allocation, and flexible accounting mechanisms.
Another emerging communication protocol for AAA is the Common Open Policy Service (COPS) query-and-response protocol. COPS is a policy and control protocol linking Policy Decision Points (PDP) and Policy Enforcement Points (PEP). Like DIAMETER, COPS is scalable, and COPS can be configured to support different policy-based services to provide general administration, configuration, and enforcement mechanisms on communication network systems. COPS can be used to support AAA and runs under TCP.
An advantage of COPS is its interoperability across all wireless communication systems, permitting wireless roaming over different communication standards (e.g. 802.11, CDMA2000, UMTS, GSM, etc). The COPS architecture creates a “protocol gateway” effectively translating data among networks using different protocols into a single, common language. Defined message types in COPS include Request, Response, Report State, Synchronize State, Client-Accept, Client-Close, and Keep-Alive.
The 3rd Generation Partnership Project 2 (3GPP2) is an evolving third generation communication system standard for wireless communication systems transmitting multimedia services. These 3GPP2 mobile communication systems support multimedia telecommunication services delivering voice (VoIP) and data, to include pictures, video communications, and other multimedia information over mobile wireless connections. These systems generally operate over a derivative General Packet Radio Service (GPRS) and/or Universal Mobile Telecommunication Systems (UMTS) communication system architecture.
Multimedia communications over 3GPP2 systems use Session Initiation Protocol (SIP) to setup communication paths over the system's router for transmitting information packets. SIP is the core protocol for establishing multimedia communication sessions in the Internet. The protocol transmits information packets establishing, changing, and terminating communication sessions for multimedia applications in IP-based networks. The protocol is used to register IP-based address end points; perform address resolution, name mapping and call redirection functions; determine media capabilities of the target end points; register end user preferences and call routing; register and publish presence information; establish a communication session and support mid-session changes; and support transfer and termination of calls.
Currently, there is no control interface between the access gateway and the SIP proxy server on the 3GPP2 systems featuring SIP for setting up appropriate communication interfaces on the system's routers. If service for the communication session over the wireless connection is disrupted, the access gateway receives indication of the service loss. However, since the access gateway and the SIP proxy server lack an appropriate interface, the SIP proxy server does not receive an indication of the loss in service and continues reservation of network resources that support a lost communication session with the mobile station. Without notification to and from the SIP proxy server and the serving SIP server, network resources remain allocated to the discontinued session on the communication network. Timely notification to the proxy and serving SIP server will free network resources and terminate AAA features thereby improving efficiency and usage data accuracy.